Patent GB-713078-A (GB)
Title: Improvements in or relating to photographic contact printing machines for preparing photo-mechanical printing surfaces
Inventor: COOK FRANCIS FREDERICK
IPC: G03F7/20
Filed: 1951-04-27
Abstract: 713,078. Photographic contact-printing apparatus. PICTORIAL MACHINERY, Ltd. April 23, 1952 [April 27, 1951], No. 9968/51. Class 98(2) A photographic step-and-repeat contact printing machine for preparing photo-mechanical printing surfaces incorporates a braking device for holding the carriage at its set position on the bed comprising in combination a stationary brake track extending parallel to the plate of the carriage, a brake mechanism fixed to the carriage and incorporating a braking element sliding on the track, and operating means for bringing and releasably holding the braking element in gripping contact with the track; in this machine the brake track consists of a rigid bar supported only at its ends, the operating means consists of a screw threaded into a guide so that the screw may be turned to apply a thrust to the braking element in a direction substantially normal to the brake track, and the brake mechanism is provided with support means adjacent the braking element for supporting the bar against flexing an application of the braking thrust by the screw. As shown in Fig. 4, a carriage 13 slidable on a fixed bed (not shown) carries a bracket 14 comprising a plate 15 and a forked portion 17. A rod 11, fixed parallel to the bed, passes through the forks of portion 17, and a collar 20 is loosely mounted on rod 11 between the forks. Collar 20 has a rotatable eccentric inner sleeve 21 embracing rod 11. Part of the collar 20 is cut away to allow a tommy bar to be inserted in holes 22 in sleeve 21, which may thus be rotated. To lock the sleeve, collar 20 is split radially at 70 and may be tightened by a screw 71. The bridge 72 of the forked portion 17 is threaded to receive a screw 24 having a pointed end 25 engaging a depression 26 in the collar 20. The shank of the screw passes through a sleeve 29 slidable in a bridge 18 formed on the bracket 14. This sleeve has an eccentric cam with a domed under-surface 74 formed below the bridge 18, and is forced upward by a spring 32 surrounding the shank of the screw. The upper end of the sleeve has opposed tongues 33 of rectangular shape separated by two wedge-shaped cams 34. A handle 38 has a forked boss 37 pivoted to the flattened upper end of screw 24 and having V-shaped notches engaging cams 34. By turning handle 38, in a horizontal plane, screw 24 can be advanced to press collar 20 and so clamp carriage 13 to the rod 11. Handle 38 can then be swung in a vertical plane, whereby the notched fork of boss 37 acts on cams 34 to move sleeve 29 down. Provided the handle 38 has first been turned into clamping position, cam surface 74 acts on a rod 41, Fig. 2, slidable in a bore in the bracket 14, moving it outwardly against a slide 43 slidable in a fitting 44 on the carriage. Slide 43 has a cam surface bearing on a ball 46 in a housing 47. As the ball moves it moves a plunger 49 against action of a spring 52. A stop 54 is adjustably fixed to the machine bed. When the carriage is moved, the stop rides over the inclined end 51 of plunger 49 and is engaged between the plunger and a spring-urged pivoted lever 57, holding the carriage in position for an exposure. After the exposure, handle 38 is moved horizontally to clamp the carriage, and then vertically to allow stop 54 to be moved to a new position. The carriage can then be unclamped and moved to a new position engaging the stop for the next exposure.